a) Field of the Invention
The present invention relates to a female screw member, a motor operated valve using the female screw member, and a method for producing the female screw member for the motor operated valve.
b) Description of the Conventional Art
As a motor operated valve used for controlling the flow rate of a refrigerant or the like in a refrigerating cycle system, Japanese unexamined patent publication No. 2006-70990 discloses the motor operated valve having a driving mechanism configured to contact/separate a valve body with/from a valve seat by utilizing rotation of a rotor of an electric motor. In such motor operated valve, when the valve is in fully closing, an upper stopper body fixed on a valve shaft holder collides with a lower stopper body fixed at a guide bush to stop rotation and downward movement of the valve shaft. The motor operated valve adopts such a screw removing structure that in a fully opening direction, the valve shaft holder is finally unscrewed from the guide bush fixed at the valve main body to stop upward movement of the valve shaft.
However, the screw removing structure in the fully opening direction like the above described motor operated valve cannot be adopted for a motor operated valve having a configuration that the valve shaft holder cannot be unscrewed from the guide bush.
On the other hand, Japanese examined patent publication No. H6-94910 discloses an electric control valve provided with a valve part including a valve seat and a valve body, a stepping motor part, which is positioned in the upper direction of the valve part and contacts/separates the valve body with/from the valve seat by a rotation of a rotor. This electric control valve includes a fully opening stopper for restricting the movement of valve body to a fully opening position of the valve, and a fully closing stopper for restricting the movement of valve body to a fully closed position of the valve, and these stoppers are provided in the upper direction of the rotor in a closed casing.
However, in the above-described electric control valve, since the fully opening and closing stoppers are positioned in the upper direction of the rotor, the entire length of the electric control valve comes to be long. In addition, since the number of parts used for the fully opening and closing stoppers increases, there is a problem that the operability for the assembly of the valve is degraded so that a manufacturing cost increases. Further, if such the fully opening and closing stoppers are to be provided in the rotor, it is necessary to decrease an outer diameter of the shaft valve holder in order to provide an installation space. Accordingly, it comes to be difficult to secure installation or setting space for a coil spring for urging the valve body. Therefore, it has been difficult to downsize the motor operated valve while maintaining a large valve aperture.
Thus, the applicant of the present application has proposed a motor operated valve with reduced number of parts, having an easily assembled structure, and capable of maintaining a large valve aperture even if downsizing, in Japanese patent application No. 2009-11549, which was published on Aug. 5, 2010, as Japanese unexamined patent publication No. 2010-169173.
As illustrated in FIGS. 7A to 7E, the motor operated valve according to such prior proposed invention is provided with a valve main body 55 including two conduits 52 and 53 and a valve seat 54, a can 56 connected with the valve main body 55, and a rotor 57 arranged inside the can 56 and forming a part of an electric motor. The motor operated vale is further provided with a stator (not illustrated) fixed at an outer peripheral part of the can 56 and rotating/driving the rotor 57, a male screw member (valve shaft) 60 connected integrally to the rotor 57 via a supporting ring 59, and a female screw member (valve shaft holder) 61 whose lower end part is fixed at the valve main body 55 via a joint ring 65, where the male screw member 60 is inserted into the female screw member 61. The motor operated valve is further provided with a valve body 62 being locked at a lower end part of the male screw member 60 and contacting to/separating from a valve seat. In addition, FIG. 7A illustrates a cross-sectional view when fully closing, and FIG. 7B illustrates a cross-sectional view when fully opening. Furthermore, FIGS. 7C to 7E and FIGS. 8A to 8C illustrate the female screw member 61 integrally molded with the joint ring 65.
With the aforementioned configuration, when an operator desires to close the motor operated valve 51, an electric current is made to flow in the stator in one direction so as to magnetically excite the stator, in a state illustrated in FIG. 7B, so that the rotor 57 rotates in a clockwise direction as viewed from an upper side. Simultaneously, the male screw member 60 rotates and goes down while threadedly connecting a male screw 60a to a female screw 61a, and the valve body 62 sits down on the valve seat 54. Then, the motor operated valve 51 is closed.
At a time when the valve body 62 sits down on the valve seat 54, a fully closing upper stopper part 59a does not reach to a fully closing lower stopper part 61d, and the rotor 57 is in a further rotatable state. The rotor 57 further rotates in a clockwise direction as viewed from an upper side, and when the fully closing upper stopper part (fully closing movable stopper for restricting the movement of valve body to a fully closing position of the valve) 59a is in contact with the fully closing lower stopper part (fully closing fixing stopper for restricting the movement of valve body to a fully closing position of the valve) 61d, the rotation of the rotor 57 is forcibly stopped.
Further, when the valve body 62 sits down on the valve seat 54, the male screw member 60 further goes down although the valve body 62 stops moving. Thus, the coil spring 64 is compressed to press the valve body 62 toward the valve seat 54, and an operation ends with a state illustrated in FIG. 7A.
On the other hand, when an operator desires to open the motor operated valve 51, an electric current is made to follow in the stator in an opposite direction to the above mentioned direction so as to magnetically excite, in a state illustrated in FIG. 7A, so that the rotor 57 rotates in the counterclockwise direction as viewed from upper direction. Then, the male screw member 60 also rotates and goes up while screwing the male screw 60a to the female screw 61a, and the valve body 62 is separated from the valve seat 54, so that the motor operated valve is opened. Further, the rotor 57 further rotates, and when the fully opening lower stopper part (fully opening movable stopper for restricting the movement of valve body to a fully opening position of the valve) 67 is in contact with the fully opening upper stopper part (fully opening fixing stopper for restricting the movement of valve body to a fully opening position of the valve) 61f, the rotation of rotor 57 stops, and the up going of valve body 62 also stops.
As mentioned above, according to the motor operated valve 51 of the prior proposed invention by the applicant, the female screw member 61 is integrally molded with the two stopper parts 61d and 61f functioning at times of the fully opening and the fully closing of the motor operated valve 51. Thus, the downsizing of the motor operated valve 51 comes to be possible, and the number of parts decreases. In addition, since the female screw member 61 is integrally molded with the two stopper parts 61d and 61f, the positional relationship between the two stopper parts 61d and 61f can be stabilized, so that assembling can be improved.
However, in the motor operated valve 51 according to the prior proposed invention by the applicant, as illustrated in FIG. 9, when the joint ring 65 is insert-molded so as to produce the female screw member 61 and the joint ring 65 by using one core 70, the stopper part 61f comes to be an undercut, so that the core 70 comes to be non-rotatable. In other words, although FIG. 9 illustrates a state that the female screw member 61 is molded by using the core 70, if the core 70 is rotated to be taken out downward after the female screw member 61 is molded, the core 70 cannot be rotated since the stopper part 61f exists, so that the core 70 cannot be taken out downward.
Therefore, as illustrated in FIGS. 10A to 10B, two cores 73 and 74 (a core 73 to form a female screw 61a, and a core 74 to form a cylindrical part with a large diameter which is formed continuously to the female screw member 6a) are used in addition to an upper mold 71 and a lower mold 72. After the core 73 is fixed to the core 74, these cores 73 and 74 are arranged inside the upper mold 71 and the lower mold 72. After a joint ring 65 is insert-molded, the core 74 and the core 73 are taken out in this order, more specifically, after or while the core 74 is removed, the core 73 is rotated to be taken out. Accordingly, an inner wall face of the female screw member 61a can be molded while avoiding the undercut of the stopper part 61f. However, in such a production method, it is difficult to completely align cores between the cores 73 and 74. Thus, misalignment may occur between the female screw 61a of the female screw member 61 and the lower end part 61c. Therefore, there is a problem that integrating the female screw member 61 with the male screw member 60 is difficult (refer to FIGS. 7A to 7E).
Further, a space may be formed between the cores 73 and 74. When the space is formed, a burr is generated at the space portion, and an operation to remove the burr is necessary. So, there is a problem that the production cost of the motor operated valve 51 increases. Although the core 74 can be integrated with the lower mold 72, there is a similar problem to the aforementioned problem in such a case.